Photoshop zoom resolution problem

It all started when I updated Photoshop CC from 2016 to 2018. I went to create a new document for drawing (I use a Wacom tablet) and the brush tool was pixelated. The document was 2500 x 2500 pixels with 300 dpi. I found this odd, so I opened up a Default Photoshop Size document preset and the brush tool and resolution of the document was fine. There was nice smooth lines when I drew. When I reopened my 2500 x 2500 custom document, the brush was still pixelated. I played around with settings in Photoshop for hours and looked online to see if anyone else was having a similar issue. No luck. However, when I went to the "View" tab and pressed "Zoom In" on my custom 2500 x 2500 document, the resolution of the whole document changed and my lines became smooth. When I zoomed in and out using the "View" tab the resolution of my lines changed. What's even more odd is that my Wacom tablet has zoom hotkeys and whenever I zoomed in or out using the hotkeys, the resolution of the lines stayed the same (either pixelated or smooth). Only when I zoom in or out using the "View" tab does the resolution of the brush tool change. So now, whenever I want to use a custom document size the first thing I have to do is go to the "View" tab and zoom in to fix the resolution of my document. Very odd. Some document sizes require me to zoom in with the "View" tab while others start out with smooth lines. What is the problem with the software? Why does the zoom tab fix the resolution problem?